Drilling tool

ABSTRACT

A drilling tool for drilling in metals has in its front part cutting insert-carrying cartridges, for instance 3, 5 or 7 in number. The peripheral cartridge (6) carries a peripheral cutting insert (7). This peripheral cartridge is fastened in the drill by a locking screw (16) that extends in a slot (17) in the drillhead. Radially inside of the peripheral cartridge is a wedge (15) which can be displaced axially and thereby regulate the radial position of the peripheral cartridge and cutting insert and, thereby, the cutting diameter. When the desired radial adjustment has been attained, the peripheral cutting insert is fixed by the locking screw (16). In this way, a very exact adjustment of the cutting diameter is obtained.

The present invention relates to a drilling tool in first hand intendedfor drilling in metals, comprising a peripheral cutting insert mountedin an adjustable cartridge for adjusting the cutting diameter:, inaccordance with claim 1.

For drills it is known to use cutting inserts of cemented carbide whichare fastened on the drill by mechanical clamping arrangements. Inaccordance with a number of known constructions, the cutting inserts arefirst mounted in cartridges, which thereafter are mechanically andreversibly fastened in the drill. For instance, in U.S. Pat. No.3,726,352 (& SE-C-347 673) such a construction is described, accordingto which the cutting diameter is adjusted by positioning the peripheralcartridge by means of two set screws. When the desired diameter has beenattained, the cartridge is fixed by a special locking screw. Althoughthis construction has functioned satisfactorily, experience over theyears has revealed several inconveniences. The use of two set screwsproduces inaccuracies in the cutting diameter. Further, the range ofadjustment is very narrow, more precisely in the order of magnitude ofup to 0,1 mm. This depends on one hand on the fact that the lockingscrew is accomodated in a bored-up hole in the drill, the play betweenthe wall of said hole and the locking screw determining the radialadjustment range of the cartridge, and on the other hand that it is notpossible to co-adjust the support pads of the drill in relation with theperipheral cutting insert. A further disadvantage of this constructionis that it is necessary to loosen the locking screw completely when itis desired to take away the cartridge from the drillhead.

A primary object of the present invention is to provide a drilling toolthat makes possible a safer, simpler and more accurate adjustment of thecutting diameter than hitherto known drilling tools do.

A second object of the present invention is to simplify the detachmentof the cartridges.

These and further objects have been attained by forming the peripheralcartridge of the drilling tool with a slot and a wedge in accordancewith the characterizing clause of claim 1.

For illustrative but non-limiting purposes, the invention will now befurther described with reference to the appended drawings, which show apreferred embodiment of the invention.

FIG. 1 shows a drilling tool according to the invention in a perspectiveview obliquely from above, one cartridge being shown in an explodedview.

FIG. 2 shows an exploded view of the peripheral insert seat of adrilling tool according to FIG. 1.

FIG. 3 shows a perspective view of the peripheral cartridge obliquelyfrom above, as seen towards the radially inner side.

FIG. 4 shows a drilling tool according to the invention in a side view,partly in cross-section.

FIG. 5 shows a top view of the drilling tool according to FIG. 4.

FIG. 6 shows a support pad which suitably is included in the drillingtool according to the invention.

FIG. 7 shows a support pad seat in a drilling tool according to theinvention.

In FIG. 1 a drilling tool according to the invention is generallydesignated by reference numeral 1. Suitably, the drilling tool is ofejector type but may advantageously be used generally at so calledBTA-drilling. It comprises a crown or drillhead 2, a dimension adapter 3and a shaft part 4. This shaft part is provided with an external thread5 which is intended to be screwed into an outer holding tube (not shown)in a way known per se.

The illustrated drilling tool is equipped with three insert-carryingcartridges: a peripheral cartridge 6 with a peripheral cutting insert 7,an intermediate cartridge 8 with an intermediate cutting insert 9 and acentral cartridge 10 with a central cutting insert 11. The peripheralcutting insert 7 produces the diameter in the hole of the machinedworkpiece. The adjacent central cutting insert 11 overlaps the centralaxis of the drill since no remaining core is desired. At rotation, theorbit of the cutting edge of the intermediate cutting insert 9 overlapswith the cutting edges of both the peripheral and the central cuttinginsert in order to obtain a continuous cutting line from the centralaxis to the periphery.

The number of cutting inserts in the drilling tool may be larger orsmaller than three. Thus, the drilling tool may for instance be madewith 4 to 9 cutting inserts, an uneven number of cutting inserts beingpreferred when the drill comprises two support pads. It has for instancebeen found that the number three is a good compromise betweencomplicity, useful life and balancing for cutting diameters between 20and 105 mm.

Two chip flutes open to the top side of the drill: one common, largerchip flute 12 for the peripheral and central cutting inserts, and onesomewhat smaller chip flute 13 for the intermediate cutting insert. Thelower, opposite ends of these chip flutes preferably open into aturned-up inner chip space 14 (see FIG. 4) which has the form of afrustocone with the bottom surface turned upwards towards the top sideof the drill.

According to the present invention, the peripheral cartridge 6, andthereby the operative cutting edge of the peripheral cutting insert 7,is radially adjustable by means of a wedge 15, the locking screw 16 ofthe cartridge being accomodated in a slot 17. Contrary to a cylindricalhole, this slot has two essential advantages: on one hand, the lockingscrew 16 may be moved radially in the slot when adjusting the cuttingdiameter, and on the other hand the whole cartridge may be removed fromthe drilling tool by simply turning or rotating the locking screw 16through only a few revolutions (i.e., the locking screw need not becompletely removed). In order to further secure the peripheral cartridgeagainst centrifugal forces, the slot 17 may be shaped in such a way thatits length y increases radially outwardly. In this way, the peripheralcartridge cannot be flung radially outwards once the locking screw 16has been tightened. Further, the locking screw 16 is preferrably angledradially inwardly relative to the peripheral tangent of the drillingtool, as may be seen in FIG. 5, to permit a distinct abutment betweenthe underside of the screw's head and the corresponding abutment surfaceabove and underneath the slot opening, respectively.

The wedge 15, which is essential for the present invention, has athickness that tapers in a narrowing manner axially downwards. It abutsagainst the axially oblique, radially inwardly directed slide abutmentsurface 18 (see FIG. 3), which suitably is inclined between 3° and 25°relative to the drill's central axis or axis of rotation. The wedge isscrewed upon the cartridge by a screw 19 which is inserted through ahole 20 in the cartridge. The hole 20 is elongated in axial direction inorder to enable an axial displacement of the wedge and, thereby, aradial fine adjustment of the peripheral cutting insert. The axial angleof surface 18 is substantially equally large as the angle between thetwo main surfaces of the wedge 15, so that the side of the wedge thatlies against the cartridge seat 30 is substantially situated in an axialplane, like the bottom surface of the cartridge seat. When the desiredcutting diameter has been attained, the peripheral cartridge is fixed inthat position by the locking screw 16. The threaded hole for the lockingscrew 16 in the cartridge may either be blind or through.

Preferably, the radially inner side of the peripheral cartridge is atits lower part formed with a planar abutment surface 29, which at leastto some extent always rests against a corresponding surface part in thedrill's cartridge seat 30. Hence, at a positioning of the peripheralcutting edge, the cartridge is tilted around a point or line at thelower part of the cartridge. This line will normally be the upper orlower longitudinal edge line of the abutment surface 29.

According to a preferred embodiment of the present invention, also theother cartridges, i.e., in this case the intermediate and centralcartridges, are shaped with slots instead of through holes, eachintended to accomodate a locking screw. Thus, as may be seen in FIG. 1,the intermediate cartridge 8 is provided with a slot 21, through whichextends the locking screw 22. The slot has a shoulder 23 against whichthe bottom surface of the locking screw's head rests. Starting off fromthe opening of the slot, this shoulder is inclined axially downwardly inorder to lock the cartridge tangentially when the locking screw istightened. The central cartridge is formed in a corresponding way.

In order to support and guide the drill in the drillhole, the drill isprovided with two support pads 24 of cemented carbide. The peripheralcartridge 6 is also provided with a supporting shim 31 of a suitablematerial, such as bakelite. According to a preferred embodiment, thesupport pads 24 have a substantially parallelepiped basic shape with arectangular plane view. Preferably, they are provided with twowing-shaped outgrowths 25, one at each longitudinal side. Theseoutgrowths have substantially the shape of two circle segments, whichbasically constitute each other's reflected images, and whose outercontour essentially corresponds to a circle line. Their extensionsuitably constitutes between 1/5 and 3/5 of the total length of thelongside, preferably between 1/4 and the half. The radially outer side17 of the support pads is somewhat rounded to abut against the drilledhole in the workpiece. Further, the support pad shows a through centralhole 18 for the fixing of the support pad in the drill hole by asuitable locking screw.

FIG. 7 shows a seat 27 for accomodating the support pad. The seat 27 hasa substantially plane bottom. The two axial delimitations have twobulging portions 28, whose shape basically corresponds to thegeometrical form of the outgrowths 25. In this way, the support pad maybe turned half a revolution if one of the shortends has been damaged,since the shortends do not have to function as abutment surfaces.Further, by means of underlying shim layers of differing thicknesses,different diameters may easily be adjusted, depending upon which cuttingdiameter has been set for the peripheral cutting insert. Then these shimlayers have a plane view that substantially corresponds to the supportpad and are laid under the support pad as distance elements. Moreover,the entire support pad seat 27 can be produced by one single end mill.

The construction according to the invention has brought a number ofadvantages in comparison with previously known constructions. Thus, avery simple as well as very safe adjustment of the cutting diameter hasbeen attained. Inter alia, this has been accomplished by the fact that awedge with a screw gives a stiff construction, since the contact surfaceis large, and thereby, a more accurate adjustment. Furthermore, theadjustment is simplified by the fact that a larger displacement axiallyresults in a small diametrical displacement. Moreover, the peripheralcartridge can be detached in a very simple way.

It is claimed:
 1. Drilling tool comprising a peripheral cartridge thatcarries a peripheral cutting insert which determines the cuttingdiameter, wherein on the radially inner side of the peripheral cartridgeis arranged a wedge which can be displaced axially and thereby move theperipheral cartridge radially in order to adjust the cutting diameter,and in that the cartridge is fixed in the desired position by a lockingscrew which extends in an open slot in the drilling tool and is screwedinto a threaded hole in the peripheral cartridge, the slot being angledrelative to the radius of the tool and increasing in length radiallyoutwards in order to secure the peripheral cartridge against centrifugalforces.
 2. Drilling tool according to claim 1, wherein it comprisesbetween one and seven insert-carrying cartridges.
 3. Drilling toolaccording to claim 1 wherein, all insert-carrying cartridges except theperipheral cartridge are provided with an open slot, through which alocking screw is threaded.
 4. Drilling tool according to claim 1,wherein the wedge is fastened by a screw that extends in an axiallyelongated hole in the peripheral cartridge.
 5. Drilling tool accordingto claim 1, wherein the wedge rests upon an axially inclined slideabutment surface on the radially inner side of the peripheral cartridge,the wedge angle of said surface and the wedge being so adjusted that theradially inner side of the wedge is substantially parallel to an axialextension of the tool.
 6. Drilling tool according to claim 1, whereinone or several support pads are arranged around the periphery of thedrilling tool in order to support and guide the drill in the drillhole.7. Drilling tool according to claim 6, wherein each support pad has aparallelepiped basic shape with a rectangular plane view, there being awing-formed outgrowth on each longitudinal side, which outgrowth isarranged to fit into a corresponding bulging in a support pad seatprovided in the drilling tool.
 8. Drilling tool according to claim 1,wherein down at its bottom, the radially inner side of the peripheralcartridge is provided with a plane abutment surface, which is arrangedto always rest upon the corresponding surface portion in the cartridgeseat of the drill.
 9. Drilling tool according to claim 1, wherein theradially outer side of the peripheral cartridge is provided with asupport element in order to support and guide the drilling tool in thedrillhole.
 10. Drilling tool according to claim 1, wherein the drillingtool comprises between three and five insert-carrying cartridges.